At present, the lasing wavelengths of semiconductor lasers commonly used as image exposure units in the electrophotographic field are long wavelengths of 650 to 820 nm. Accordingly, electrophotographic photosensitive members that have high sensitivity to light of the long wavelengths have been developed. In addition, in order to achieve a higher resolution, electrophotographic photosensitive members that have high sensitivity to light emitted by semiconductor lasers having short lasing wavelengths have been developed recently.
Phthalocyanine pigments are known as charge generation substances that have high sensitivity to light of wavelengths across the long wavelength region to the short wavelength region. In particular, oxytitanium phthalocyanine and gallium phthalocyanine have high sensitivity characteristics and various crystal forms thereof have been reported.
An electrophotographic photosensitive member including a gallium phthalocyanine pigment has high sensitivity characteristics; however, dispersibility of gallium phthalocyanine pigment particles is poor, which is problematic. For this reason, an improvement is necessary to obtain a charge generation layer-coating solution containing this pigment and having high coatability.
In a case where a charge generation layer-coating solution does not have sufficient coatability, during coating, aggregation of pigment particles tends to result in generation of spots (blue spots) or occurrence of coating unevenness in the charge generation layer. Blue spots in a charge generation layer may cause black spots or fogging particularly in output images. On the other hand, coating unevenness in a charge generation layer causes image density unevenness particularly in halftone image formation areas, resulting in degradation of image quality.
Patent Literature 1 states that gallium phthalocyanine and a polyvinylalcohol resin having a specific structure are used to thereby achieve enhancement of coatability and stability of the coating material.
In addition, Patent Literature 2 states that a photosensitive layer contains a nitrogen-containing heterocyclic compound such as morpholine, piperazine, or piperidine to thereby enhance resistance to ozone and resistance to NOx. However, Patent Literature 2 does not describe anything about dispersibility or coatability.
Furthermore, Patent Literature 3 describes a hydroxygallium phthalocyanine crystal obtained by milling treatment using N-methylformamide, N,N-dimethylformamide, N-methylacetamide, and N-methylpropionamide. However, Patent Literature 3 does not describe anything about dispersibility or coatability.